The present invention relates to display applications, and in particular, to flexible displays.
Many applications can benefit from inclusion of a display. For example, projection devices, sketching apparatuses, telephones, pocketbooks, and battery indicators are only a few applications that display transient information. To date, widespread incorporation of displays has been hindered because such applications generally require flexible displays that consume very little power.
Despite much effort directed to developing highly-flexible, reflective display media, there are relatively few examples of displays formed on semi-flexible substrates, and these examples have found only moderate success. For example, plastic-based liquid crystal displays, including twisted nematic (TN), supertwisted nematic (STN), polymer dispersed liquid crystal (PDLC), and bistable cholesteric liquid crystals have been developed. Nevertheless, problems remain with liquid crystal alignment in TN and STN displays, cholesteric displays are sensitive to changes in their cell gap, and local stress can cause changes in the scattering or absorbance of PDLC and cholesteric films. As such, only moderate flexibility can be achieved with these displays.
Emissive electroluminescent films and organic light emitting diode films can be deposited on flexible substrates to create flexible displays. However, these devices require continuous power consumption for operation, and thus are not practical for many applications.
Another problem with developing highly flexible displays is the lack of an appropriate conductor for addressing the display elements. Typically, an indium tin oxide (ITO) layer vacuum sputtered onto a plastic substrate is used as a top conductor for displays. An ITO layer, however, can be damaged when the display is flexed. If the local curvature of the plastic substrate becomes too great, the ITO layer tends to crack, damaging the display.
An object of the invention is to provide a highly-flexible, reflective display which can be manufactured easily, consumes little (or no in the case of bistable displays) power, and can, therefore, be incorporated into a variety of applications. The invention features a printable display comprising an encapsulated electrophoretic display medium. The resulting display is flexible. Since the display media can be printed, the display itself can be made inexpensively.
An encapsulated electrophoretic display can be constructed so that the optical state of the display is stable for some length of time. When the display has two states which are stable in this manner, the display is said to be bistable. If more than two states of the display are stable, then the display can be said to be multistable. For the purpose of this invention, the term bistable will be used to indicate a display in which any optical state remains fixed once the addressing voltage is removed. The definition of a bistable state depends on the application for the display. A slowly-decaying optical state can be effectively bistable if the optical state is substantially unchanged over the required viewing time. For example, in a display which is updated every few minutes, a display image which is stable for hours or days is effectively bistable for that application. In this invention, the term bistable also indicates a display with an optical state sufficiently longlived as to be effectively bistable for the application in mind. Alternatively, it is possible to construct encapsulated electrophoretic displays in which the image decays quickly once the addressing voltage to the display is removed (i.e., the display is not bistable or multistable). As will be described, in some applications it is advantageous to use an encapsulated electrophoretic display which is not bistable. Whether or not an encapsulated electrophoretic display is bistable, and its degree of bistability, can be controlled through appropriate chemical modification of the electrophoretic particles, the suspending fluid, the capsule, and binder materials.
An encapsulated electrophoretic display may take many forms. The display may comprise capsules dispersed in a binder. The capsules may be of any size or shape. The capsules may, for example, be spherical and may have diameters in the millimeter range or the micron range, but is preferably from ten to a few hundred microns. The capsules may be formed by an encapsulation technique, as described below. Particles may be encapsulated in the capsules. The particles may be two or more different types of particles. The particles may be colored, luminescent, light-absorbing or transparent, for example. The particles may include neat pigments, dyed (laked) pigments or pigment/polymer composites, for example. The display may further comprise a suspending fluid in which the particles are dispersed.
The successful construction of an encapsulated electrophoretic display requires the proper interaction of several different types of materials and processes, such as a polymeric binder and, optionally, a capsule membrane. These materials must be chemically compatible with the electrophoretic particles and fluid, as well as with each other. The capsule materials may engage in useful surface interactions with the electrophoretic particles, or may act as a chemical or physical boundary between the fluid and the binder.
In some cases, the encapsulation step of the process is not necessary, and the electrophoretic fluid may be directly dispersed or emulsified into the binder (or a precursor to the binder materials) and an effective xe2x80x9cpolymer-dispersed electrophoretic displayxe2x80x9d constructed. In such displays, voids created in the binder may be referred to as capsules or microcapsules even though no capsule membrane is present. The binder dispersed electrophoretic display may be of the emulsion or phase separation type.
Throughout the specification, reference will be made to printing or printed. As used throughout the specification, printing is intended to include all forms of printing and coating, including: premetered coatings such as patch die coating, slot or extrusion coating, slide or cascade coating, and curtain coating; roll coating such as knife over roll coating, forward and reverse roll coating; gravure coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; silk screen printing processes; electrostatic printing processes; thermal printing processes; and other similar techniques. A xe2x80x9cprinted elementxe2x80x9d refers to an element formed using any one of the above techniques.
In one aspect, the invention features an indicator. The indicator includes a substrate, a transducer, and an electrically addressable display printed on the substrate in electrical communication with the transducer. The transducer is, in some embodiments, printed on the substrate and, in other embodiments, is conventionally disposed on the substrate. The display shows a change in optical state in response to a signal from the transducer. In one embodiment, the indicator is a battery indicator. The battery indicator is in electrical communication with a battery and comprises an electrically addressable display printed on the battery. The optical state shows a first value in response to a voltage of the battery. In one detailed embodiment, the battery indicator includes an electrophoretic display comprising a microencapsulated display media, a first electrode and a second electrode disposed adjacent the electrophoretic display, a nonlinear element, a voltage divider, and a resistor. The first and second electrodes apply an electric field to the electrophoretic display media. The nonlinear element is in electrical communication with a battery and the first electrode. The nonlinear element conducts a battery voltage to the first electrode when the battery voltage exceeds a predetermined threshold. The voltage divider is in electrical communication with the battery and the second electrode. The voltage divider provides a voltage to the second electrode that is less than the battery voltage. The resistor is in electrical communication with the nonlinear element and the voltage divider.
In another aspect, the invention features a sticker display. The electrically active sticker display includes an encapsulated display media and an adhesive layer disposed on the first surface of the display media. In some cases, the encapsulated electrophoretic display may be itself sufficiently adhesive to function as a sticker without additional adhesive layers. The display media comprises an optoelectrically active material. In one embodiment, a transparent layer including an electrode is disposed adjacent a surface of the display media. In another embodiment, the sticker display further includes a via which extends from the transparent layer to the adhesive layer.
In still another aspect, the invention features a method of printing an electrically active display. The methods comprises the steps of: (a) providing a film having a clear electrode structure disposed on a first surface of the film; (b) printing a display media on the first surface of the film; and (c) printing or laminating a second electrode covering at least a portion of the display media. The display media comprises an encapsulated optoelectrically active material dispersed in a binder
In still another aspect, the invention features a radio-controlled display. The radio controlled display includes an electrically active display having an encapsulated display media, a receiver, and a decoder in electrical communication with the receiver. The display is responsive to the output of the decoder. In one embodiment, the display further includes a power source in connection with the display. In another embodiment, the display further includes a plurality of row and column drivers disposed on the substrate for addressing the display. In still another embodiment, the display further includes an antenna in communication with a control circuit.
In still another aspect, the invention features a process for creating an electrically addressable display. The method comprises the steps of (a) providing a substrate; and (b) printing an electrically active ink comprising at least one microcapsule dispersed in a binder onto a first area of a receiving substrate. Optical qualities of the electrically active ink are modulated responsive to broadcast signals.
In still another aspect, the invention features a process for printing an electrically addressable display. The method comprises the steps of: (a) providing a substrate; and (b) printing an electrically active ink comprising at least one microcapsule dispersed in a binder onto a first area of the receiving substrate.
In still another aspect, the invention features an electrically active display tile. The tile includes a substrate, an electrically addressable display disposed on the substrate, a controller disposed on the substrate in electrical communication with the display, and a connector disposed on the substrate for connecting the display tile to another display tile. The display comprises a encapsulated display medium. In one embodiment, the display tile further includes a receiver for receiving radio signals or other electromagnetic radiation, and the controller changes the display in response to the received radio signals. In another embodiment, the display tile further includes a memory element storing data, and the controller changes the display responsive to data stored in the memory element.
In still another aspect the invention features a wearable display. A wearable display includes an article of clothing including an electrically addressable display incorporated into the wearable item and a controller in electrical communication with the display. The display comprises an encapsulated display media. In one embodiment, the controller is incorporated into the wearable item. In another embodiment, the wearable item comprises a fashion accessory. In still another embodiment, the wearable item includes an interface for receiving information from another device that can be displayed by the wearable item, such as a temperature monitor or position-sensing device.